This invention is related to methods and systems used to determine the specific gravity, absorption, and/or porosity characteristics of compacted and loose materials including aggregate materials used in the construction of roads and structures as well as those obtained in connection with oil and geological explorations.
Water absorption and specific gravity of aggregates are both parameters which are routinely analyzed in the design and construction of roads and structures worldwide. These parameters can also be important considerations in oil and geological explorations.
The ability to accurately measure water absorption and specific gravity of materials in a repeatable manner and in a relatively short time frame can be important for engineers and practitioners interested in assessing the suitability of bulk materials and material mixtures in their projects. For example, water absorption and specific gravity values can yield important information about the hydraulic properties of soils and aggregates.
In the asphalt mix design industry, the bulk specific gravity and absorption of aggregates in a particular design, which can include both fine and coarse aggregates, are important assessments of the quality and suitability of the asphalt design to a particular application. The design selection of materials can be a mixture or composition of various sized aggregates in an assortment of different materials which can be varied to yield the desired functional characteristics or standards. Bulk specific gravity can be used as a measure to assess the amount of asphalt binder absorbed by the aggregates and the percentage of voids in the mineral aggregates in the design; each of these parameters can be important considerations in assessing the quality of the materials or the suitability of the composition of the design.
Conventionally, test methods described in standards AASHTO T84 and ASTM C128 have been used to assess fine aggregates. Unfortunately, these methods can have poor repeatability. Generally stated, the conventional method requires that a material sample of fine aggregate (about 1000 g) is oven dried to a constant weight. The material sample is then immersed in water for a 24-hour saturation period. The sample is then spread on a flat surface and exposed to a gently moving stream of warm air until a saturated surface-dry condition is reached. To assess when the saturated surface-dry condition has been reached, the material sample is positioned into an inverted cone and lightly compacted. The cone is removed and if the material xe2x80x9cslumpsxe2x80x9d the material sample is considered to be in a saturated surface-dry condition. The amount of xe2x80x9cslumpxe2x80x9d that represents when the saturated surface-dry condition has been reached can vary from test-to-test and is operator-dependent. Some laboratories or agencies define this condition as one in which the slump corresponds to the diameter of a dime from the top of the cone. The amount of slump can be adjusted by repetitive drying of the aggregates until the desired slump is achieved. However, if the aggregate sample is over-dried during the test procedure, the sample must be re-saturated and the drying process repeated.
After the material sample has reached the saturated dry-surface condition, a portion of the material sample is placed in a flask, which is then filled with water to a calibrated level and weighed. The fine aggregate material sample is removed from the flask and oven-dried to a constant weight. The specific gravity (apparent and bulk) and absorption are then calculated based on the three measured weights (the weight of the oven-dried sample, the weight of the flask filled with water, and the weight of the flask with the material and specimen and water to a calibration mark).
Angular fine aggregates with high absorption characteristics and/or rough surface textures do not typically slump readily. Therefore, determining the saturated surface dry (SSD) weight for samples that include these types of materials can be difficult with the cone method described above. Unfortunately, incorrect determination of this parameter in the testing process can have undesirable effects on the performance or service life of the asphalt pavement or other structure made using incorrectly analyzed materials.
In the concrete industry, the same cone test is typically used to determine the SSD condition in fine materials to determine the proper amount of water to add to the concrete mixture. Proportioning the concrete mixture with an incorrect amount of water can negatively affect the strength and durability of the concrete structures.
The testing standards for coarse aggregates are described in AASHTO T85 and ASTM C-127. xe2x80x9cCoarsexe2x80x9d is typically associated with aggregates retained on a 2.36 mm (No. 8) or larger sieve. In order to obtain the SSD weight of these types of samples, these standards provide that the operator pads the aggregates with a towel and uses the towel-dried weight as the SSD weight of the sample. Again, this technique is subjected to operator variability, as if the material sample is not properly preparedxe2x80x94such as if improper washing or wetting of the sample, aggressive drying, or removing fine dirt particles off the surfaces of the aggregates (thus, potentially leaving the large aggregate surface wet)xe2x80x94the results of the analysis can vary and may not provide a reliable indication of the properties of the sample. Further, the towel-dry technique itself is a subjective procedure and the degree of dryness can vary from operator-to-operator and sample-to-sample.
Recently, a study was undertaken by the National Center for Asphalt Technology (NCAT) and was presented at the 79th meeting of the Transportation Research Board, in January, 2000. In this study, the authors proposed a device to attempt to automate the determination of the SSD condition for fine aggregates as a replacement to AASHTO T84 and ASTM C128. The device included a spinning drum equipped with a hair dryer for drying the aggregates, a humidity indicator and a temperature sensor mounted inside the drum. In operation, a saturated material sample is placed inside the drum and the sample is spun while continuously monitoring temperature and humidity. The theory behind this technique is that a break in the response between temperature and time or humidity and time will indicate a saturation point. For example, continuous drying will occur until either the temperature or humidity stabilizes. At this xe2x80x9cstability pointxe2x80x9d, the aggregates are expected to be at the SSD condition. After the indicated response has stabilized, the temperature or humidity can continue to change, also indicating that the internal water has been removed (another indication that the SSD condition was achieved at the stability point). Unfortunately, in operation, the material can clump together inside the drum. When aggregates clump (fine aggregates can be particularly susceptible to clumping), the SSD condition may be unachievable. Indeed, fine aggregates can impede accurate determination of a true SSD condition as they have a tendency to stack up or attach to each other and not allow the surface of each individual aggregate to reach the desired SSD condition. Further, the stability point (defined as a plateau) in time versus temperature or humidity is an empirical derivation that may be difficult to ascertain or achieve with every aggregate type.
Recently, another device has been proposed by the Barnstead/Thermolyne Company of Boise, Idaho to determine the SSD condition of fine aggregates. This device proposes placing approximately 500 g of dry aggregates in a vibrating dish. Water is introduced into the aggregate and an infrared device monitors the surface moisture. Again, the time response versus the infrared moisture reading is plotted and a point along the response line is identified and selected as corresponding to the SSD condition of the aggregates. Unfortunately, this method is also empirically based and can depend on the type and perhaps the gradation of aggregates. Also, the fine aggregate SSD may be difficult to reliably define for every aggregate type.
Embodiments of the present invention provide systems, methods, and devices that employ vacuum-sealed material samples and liquid displacement. The material sample can be divided into two portions and weights associated with each portion can then be obtained under various conditions and used to calculate the percentage absorption, the porosity, and/or the specific gravity (for fine and coarse aggregates, the term xe2x80x9cdensityxe2x80x9d is sometimes used instead of xe2x80x9cspecific gravityxe2x80x9d). Alternatively, the same material sample portion can be serially analyzed and those results compared.
In certain embodiments, a calibration adjustment factor can be applied to the calculated percent absorption value determined as summarized above. The calibration adjustment factor can correspond to a particular aggregate type or mix being analyzed. The calibration adjustment factor can offset the amount of water that may be absorbed while the sample aggregate is wetted under water and the weight measured under water (typically, the higher absorptive materials will have higher correction factors compared to the lower absorptive materials). The calibration adjustment factor can be obtained by examining the amount of absorption as a function of time that the aggregate is exposed to a vacuum, or obtained by comparing the absorption due to an independent method.
Certain embodiments of the present invention are directed to methods of determining a material property such as the absorption or specific gravity of an aggregate material. The method comprises the steps of: (a) drying a first aggregate material sample; (b) determining the dry weight of the first aggregate material sample; (c) placing the first aggregate material sample in liquid in a first container; (d) adding liquid to the container with the first aggregate sample to fill the container to a desired volume; (d) measuring the weight of the first container holding the first aggregate material sample and the liquid after the step of adding liquid; (e) drying a second aggregate material sample; (f) determining the dry weight of the second aggregate material sample; (g) vacuum sealing the second aggregate sample in a second container; (h) immersing the second aggregate material sample while it is held in the sealed second container in the liquid bath; (i) opening the sealed second container as it is held immersed in the liquid bath; (j) measuring the weight of the second aggregate material sample and the second container while they are held immersed in the liquid bath; and (k) determining at least one material property of the aggregate undergoing analysis based on the weights obtained in the two measuring steps.
In certain embodiments, the first and second samples are different samples of substantially the same weight selected such that they are both representative of the aggregate material undergoing analysis. In other embodiments, the first and second samples are the same sample of the aggregate material undergoing analysis.
Other embodiments are directed to methods for analyzing material properties of a material sample comprising aggregate. The method includes: (a) providing a first and second aggregate material sample of a material undergoing analysis; (b) drying the first aggregate material sample; (c) determining the dry weight of the first aggregate material sample; (d) providing a volumetric container, the volumetric container having a lid that attaches thereto to define a fixed internal volume of the volumetric container; (e) partially filling the volumetric container with liquid; (f) placing the first aggregate material sample in the volumetric container; (g) adding additional liquid to the container after the first aggregate material is placed in the volumetric container; (h) attaching the lid onto the volumetric container to enclose the liquid and aggregate material therein; (i) measuring the weight of the volumetric container holding the first aggregate material sample and the liquid after the steps of attaching the lid and adding additional liquid; (j) encasing the second aggregate sample in a vacuum-sealed container; (k) immersing the second aggregate material sample while it is held in the sealed container in a liquid bath; (l) opening the sealed container as it is held immersed in the liquid bath; (m) measuring the weight of the second aggregate material sample and the container while they are held immersed in the liquid bath; and (n) determining at least one of the percent absorption, apparent specific gravity, bulk specific gravity, and saturated surface dry (SSD) weight of the aggregate undergoing analysis based on the weights obtained in the measuring steps.
In particular embodiments, the lid of the volumetric container comprises a liquid entry port, and the step of adding additional liquid comprises: (a) adding a first amount of additional liquid to a level that is below the top of the volumetric container; and (b) after the step of attaching the lid, adding a second amount of liquid into the volumetric container through the liquid entry port so that the liquid with the aggregate fills the container and occupies the fixed internal volume.
Still other embodiments of the present invention are directed to methods of obtaining absorption or porosity data for an aggregate sample. The method includes: (a) providing a material specimen for analysis comprising aggregate; (b) dividing the material specimen into at least two samples, a first aggregate sample and a second aggregate sample; (c) wetting the first aggregate sample; (d) obtaining a weight of the wetted first aggregate sample; (e) encasing the second aggregate sample in a vacuum-sealed collapsible bag; (f) immersing the encased vacuum sealed second sample in liquid; (g) opening the bag while immersed to allow liquid to enter the bag; (h) obtaining a weight of the opened bag with the second sample while immersed in the liquid; and (i) evaluating the weight of the wetted first sample and the weight of the second sample in the opened bag in the liquid.
Certain embodiments of the present invention include methods of determining the absorption or porosity of an aggregate material. The method includes the steps of: obtaining a first aggregate material sample of an aggregate material undergoing analysis; obtaining a second aggregate material sample of the aggregate material undergoing analysis; drying the first and second aggregate material samples; determining the dry weight of at least one of the first and second aggregate material samples; immersing the first aggregate material sample in a liquid bath so that the first aggregate material sample is wetted; measuring the weight of the first aggregate material sample while immersed in the liquid bath; vacuum sealing the second aggregate sample in a container; immersing the second aggregate material sample while it is held in the sealed container in the liquid bath; opening the sealed container as it is held immersed in the liquid bath; measuring the weight of the second aggregate material sample and the container while they are held immersed in the liquid bath; and determining the absorption of the aggregate undergoing analysis based on the weights obtained in the first and second measuring steps.
The second material sample can be held in a collapsible vacuum-sealed bag while the first material sample can be placed in a rigid container or directly into the liquid bath container.
The method can be used for construction materials (loose or compacted) including fine and coarse aggregate materials or material mixtures as well as for porous and highly porous materials.
Other embodiments of the present invention include computer program products for determining the absorption and/or specific gravity value of an aggregate sample undergoing analysis. The computer program product includes a computer readable storage medium having computer readable program code embodied therein and comprises (a) computer readable program code for accepting input corresponding to first and second measurements of first and second aggregate sample weights corresponding to an aggregate sample undergoing analysis; and (b) computer readable program code for calculating the absorption value based on the first and second measurements.
Still other embodiments are directed to computer program products for determining absorption characteristics and/or specific gravity value of an aggregate sample undergoing analysis. The computer program product comprises computer readable storage medium having computer readable program code embodied in said medium, said computer-readable program code comprising: (a) computer readable program code for accepting input corresponding to weight measurements of first and second aggregate samples obtained under dry and different wet conditions corresponding to an aggregate sample undergoing analysis; (b) computer program code defining predetermined mathematical relationships for determining the material parameters of interest; and (c) computer readable program code for calculating at least one of the percent absorption value, the apparent specific gravity, the bulk specific gravity, the saturated surface dry weight, and the porosity, based on the dry and wet measurements of the first and second samples and the pre-determined relationships.
Additional aspects of the present invention are directed to apparatus for evaluating aggregate samples. In certain embodiments the apparatus includes a rigid volumetric container having at least one upwardly extending wall and a closed bottom and open top portion. The container may include a lid configured to securely attach to the volumetric container top portion, so that, when attached, the volumetric container and lid define an enclosed internal fixed volume. The apparatus includes a quantity of liquid and aggregate material positioned in the volumetric container. In operation, the liquid and aggregate are presented in sufficient quantity so as to occupy substantially the entire internal fixed volume and exhibit a corresponding weight.
The volumetric container or apparatus can be formed as a pycnometer device having a glass or translucent/transparent body with a reduced-size neck portion that defines an internal constant or fixed volume. The neck portion can be formed into a lid that attaches to an underlying body. The neck can be configured in the lid so that it is substantially vertically oriented and has a visible fill line marking. The neck can terminate into an open port that allows liquid to be inserted therethrough.
The apparatus can include a holding fixture. The fixture includes a planar base configured to receive the volumetric container thereon and a plurality of upwardly extending clamp platforms affixed to the base and disposed in spaced apart alignment thereon. The clamp platforms are arranged to be proximate or to abut the outside wall of the volumetric container when the volumetric container is placed on the base of the fixture. The fixture also includes at least one clamping mechanism disposed on each clamp platform. The platforms have a height sufficient to position the clamping mechanism over the top surface of the lid, such that, when in position, the clamps force the lid down onto the volumetric container.
Other embodiments of the invention are directed to systems for analyzing aggregate samples. The system includes: (a) a volumetric container with a detachable lid, the lid having a syringe access port formed therethrough; (b) a syringe having a body adapted to hold liquid therein and a lumen length sufficient to extend below the lid (and under the surface of the liquid) when in position in the access port; and (c) computer program code for determining percent absorption and specific gravity of fine or very fine aggregate samples.
Other embodiments include systems for analyzing aggregate samples that include a volumetric container with a detachable lid that together define a fixed internal volume and computer program code for determining percent absorption and/or specific gravity of aggregate samples based on a first weight obtained of the volumetric container with the lid attached and full of liquid and a second weight obtained of the volumetric container with the lid attached and full of liquid and an aggregate material sample.
Still other embodiments are directed to systems with the computer program code being selectable by the user depending on whether coarse or fine aggregates are being analyzed.
Additional embodiments are for systems for analyzing aggregate samples that include: (a) a rigid container with a detachable lid defining an internal volume; (b) at least one flow path located in an upper portion of the container; (c) a vacuum source in fluid communication with the container; and (d) computer program code for determining percent absorption and/or specific gravity of aggregate samples based on a first weight obtained of the container with the lid attached with liquid and an aggregate material sample located at a bottom portion thereof with the liquid level extending above the aggregate.
The system may include at least one valve positioned in the flow path between the container and the vacuum source.
Yet another embodiment is a system for analyzing aggregate samples comprising: (a) a container with a detachable lid defining an internal volume; (b) a pressure source in fluid communication with the container; (c) at least one flow path located in an upper portion of the container in communication with the pressure source and the container; and (d) computer program code for determining percent absorption and/or specific gravity of aggregate samples based on a first weight obtained of the volumetric container with the lid attached with liquid and an aggregate material sample located at a bottom portion thereof with the liquid level extending above the aggregate.
In particular embodiments, the pressure source is a piston. In certain embodiments, the system can include a subcontainer configured to hold the aggregate inside the container, and a scale held inside the container above the liquid level, the scale being configured with an arm that suspends the subcontainer above the bottom of the container.
The computer program product may also include one or more of computer readable program code for assigning an absorption correction factor to the calculated absorption value based on the absorption characteristics of the aggregate material undergoing analysis and code for determining the specific gravity of the aggregate material undergoing analysis based on the first and second density data input.
The techniques provided by the present invention can avoid direct determination of the mass of the sample at the SSD condition, which, as noted above, can be difficult to define with fine aggregates. Advantageously, the test methods and systems of the present invention are repeatable and can reduce or inhibit operator variability. Further, the systems and methods of the present invention can reduce the amount of active testing time, typically down to a time on the order of 10-30 minutes. A 24-hour saturation period is not required and the methods and systems can be used with both fine and coarse aggregates as well as with both high and low porosity aggregates and other material such as ceramics and other formed graded materials.
Other embodiments of the present invention include systems and methods for determining the material property characteristics of a material sample such as, apparent specific gravity or density of a material. The method includes obtaining a material sample of an construction material undergoing analysis; drying the material sample; determining the dry weight of the material sample; determining the calibrated volume of a container; placing the material sample into the container; evacuating the container with the sample held therein; introducing liquid into the container so that the material sample is held immersed under the liquid in the container after the evacuating step; measuring the weight of the material sample and the container while the sample is held immersed in the liquid in the container; and determining the apparent density of the sample based on the dry weight of the sample, the calibrated volume of the container, and the weight obtained during said measuring step.
Still other embodiments include systems and methods for determining material property characteristics of a material such as the apparent specific gravity, porosity, or absorption characteristics of a material. The embodiments can include, similar to the embodiment described above, obtaining a material sample of a construction material undergoing analysis; drying the material sample; and determining the dry weight of the material sample. The method can also include the steps of placing the material sample into subcontainer; positioning the subcontainer and the material sample in a container; introducing liquid into the container so that the material sample and the subcontainer are held immersed under the liquid in the container; measuring a first weight of the material sample and the container while the sample is held immersed in the liquid in the container at atmospheric pressure; evacuating the container with the sample held in the subcontainer positioned therein; measuring a second weight of the material sample and the container while the sample is held immersed in the liquid in the container after said evacuating step; and determining a first density and second density and/or absorption of the material sample based on the weights obtained during said measuring steps.
In another embodiment, the evacuating step can be replaced with a pressurizing step whereby the pressure in the container is elevated with the sample held in the subcontainer positioned therein and the second weight of the material sample and the container is measured while the sample is held immersed in the liquid in the container with the pressure elevated above atmospheric pressure.
Certain embodiments of the methods of the present invention may be able to assess other physical parameters associated with the material sample, such as, but not limited to, the permeability of material samples, the porosity of material samples, the apparent specific gravity, the maximum density, the maximum specific density and other related measurements or parameters. Further, the analysis may be automated so that the scales, vacuum equipment, or other machinery can be integrated to directly input desired measurement data to a computer processor that can then calculate the desired parameter and output the information to the operator.
The above summary is not intended to limit the scope of the invention as other apparatus and fixtures can also be used to carry out the methods of the present invention.
The foregoing and other objects and aspects of the present invention are explained in detail in the specification set forth below.